can we do multitasking in iphone 3g without third party softwares???

Yes it is possible because Apple iPhone device using multitasking feature on upcoming iPhone 4 and iphone 3GS (with iOS 4 software update). It allows you to use multiple third party applications on iPhone at the same time. As a result, you can do more tasks simultaneously on your iPhone device. Using multitasking is every easy through home button on iPhone

Now you can do more on your Apple iPhone device using multitasking feature on upcoming iPhone 4 and iphone 3GS (with iOS 4 software update). It allows you to use multiple third party applications on iPhone at the same time. As a result, you can do more tasks simultaneously on your iPhone device. Using multitasking is every easy through home button on iPhone.
Use ‘Home’ button for multitasking on iPhone
1. While using iPhone, double click Home button to see recently used apps.
2. You can view recently used apps at the bottom. Scroll to right to view more apps and tap anyone to open it.

The iPhone 3G is the second generation of iPhone designed and marketed by Apple Inc. . It was the successor to the original iPhone , and issucceeded by the iPhone3GS . Introduced on June 9, 2008 at the WWDC 2008 at the Moscone Center , San Francisco . The 3G was very similar to its predecessor, containing the same 2 MP camera and no support for video recording , and its performance was limited by the same 128 MB eDRAM memory unit. [ 12 ] Nevertheless, the 3G featured several improvements over the original. It supported Assisted GPS , 3G data and tri-band UMTS / HSDPA .
The iPhone 3G runs Apple’s iOS operating system, the same operating system used on prior iPhones , and the iPad , Apple TV, and iPod Touch . It is primarily controlled by a user’s fingertips on the multi-touch display, which is sensitive to fingertip contact.
The iPhone 3G no longer receives software updates from Apple. The last release of iOS to support the 3G was 4.2.1, which was released on November 22, 2010. iOS 4.3, released on March 11, 2011, did not support the iPhone 3G. Regards- ANKIT

The iPhone 3GS can now be updated to iOS 4.0, the first version of iPhone operating system to support multitasking for third-party apps. Note: For third-party apps to allow state-saving, they'll have to support iOS 4. All stock Apple apps support state-saving. The home screen button now operates as the multitasking button. All you have to do to switch between applications is double tap the home screen button (the button below the screen) twice and up will pop a dock displaying all of your recently-used apps. Simply tap on the app that you want to switch to and you can carry on where you last left off. To view all of the open applications, you can slide your finger along the dock. You can also use VoIP apps such as Skype while you're using another application. Simply double tap the home screen when on a VoIP call and you can check your emails or read the latest news headlines without disconnecting. If you're waiting for a page to load in Safari, you can just double tap the home screen button and switch to another app without Safari stopping.

The iPhone 3GS can now be updated to iOS 4.0, the first version of iPhone operating system to support multitasking for third-party apps.
Note: For third-party apps to allow state-saving, they'll have to support iOS 4. All stock Apple apps support state-saving.
The home screen button now operates as the multitasking button.
All you have to do to switch between applications is double tap the home screen button (the button below the screen) twice and up will pop a dock displaying all of your recently-used apps.
Simply tap on the app that you want to switch to and you can carry on where you last left off.
To view all of the open applications, you can slide your finger along the dock.
You can also use VoIP apps such as Skype while you're using another application. Simply double tap the home screen when on a VoIP call and you can check your emails or read the latest news headlines without disconnecting.
If you're waiting for a page to load in Safari, you can just double tap the home screen button and switch to another app without Safari stopping.

The iPhone 3GS can now be updated to iOS 4.0, the first version of iPhone operating system to support multitasking for third-party apps.
Note: For third-party apps to allow state-saving, they'll have to support iOS 4. All stock Apple apps support state-saving.
The home screen button now operates as the multitasking button.
All you have to do to switch between applications is double tap the home screen button (the button below the screen) twice and up will pop a dock displaying all of your recently-used apps.
Simply tap on the app that you want to switch to and you can carry on where you last left off.
To view all of the open applications, you can slide your finger along the dock.
You can also use VoIP apps such as Skype while you're using another application. Simply double tap the home screen when on a VoIP call and you can check your emails or read the latest news headlines without disconnecting.
If you're waiting for a page to load in Safari, you can just double tap the home screen button and switch to another app without Safari stopping.